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Introduction to Chemistry: Matter and Measurement

This chapter introduces the study of chemistry, matter, and measurement. It covers the scientific method, classification of matter, properties of matter, types of changes, and units of measurement in the metric system.

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Introduction to Chemistry: Matter and Measurement

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  1. Chapter 1 Introduction:Matter and Measurement

  2. 1.1 The Study of Chemistry

  3. Chemistry In this science we study matter and the changes it undergoes.

  4. Scientific Method The scientific method is simply a systematic approach to solving problems.

  5. Matter We define matter as anything that has mass and takes up space.

  6. Matter Atoms are the building blocks of matter. Each element is made of the same kind of atom. A compound is made of two or more different kinds of elements.

  7. 1.2 Classification of Matter

  8. States of Matter

  9. Classification of Matter

  10. Law of constant composition AKA : law of definite proportions Joseph Proust 1800 Elemental composition of a compound is always the same

  11. Sample Exercise 1.1 Distinguishing Among Elements, Compounds, and Mixtures “White gold,” used in jewelry, contains gold and another “white” metal such as palladium. Two different samples of white gold differ in the relative amounts of gold and palladium that they contain. Both samples are uniform in composition throughout. Without knowing any more about the materials, classify white gold.

  12. Practice Exercise Aspirin is composed of 60.0% carbon, 4.5% hydrogen, and 35.5% oxygen by mass, regardless of its source. Classify aspirin.

  13. 1.3 Properties of Matter

  14. Types of Properties Physical Properties… Can be observed without changing a substance into another substance. Boiling point, density, mass, volume, etc. Chemical Properties… Can only be observed when a substance is changed into another substance. Flammability, corrosiveness, reactivity with acid, etc.

  15. Types of Properties Intensive Properties… Are independent of the amount of the substance that is present. Density, boiling point, color, etc. Extensive Properties… Depend upon the amount of the substance present. Mass, volume, energy, etc.

  16. Types of Changes Physical Changes These are changes in matter that do not change the composition of a substance. Changes of state, temperature, volume, etc. Chemical Changes Chemical changes result in new substances. Combustion, oxidation, decomposition, etc.

  17. Chemical Reactions In the course of a chemical reaction, the reacting substances are converted to new substances.

  18. Compounds Compounds can be broken down into more elemental particles.

  19. Separation of Mixtures: Distillation Distillation uses differences in the boiling points of substances to separate a homogeneous mixture into its components.

  20. Filtration In filtration solid substances are separated from liquids and solutions.

  21. Chromatography This technique separates substances on the basis of differences in solubility in a solvent.

  22. 1.4 Units of Measurement

  23. SI Units Système International d’Unités A different base unit is used for each quantity.

  24. Volume The most commonly used metric units for volume are the liter (L) and the milliliter (mL). A liter is a cube 1 dm long on each side. A milliliter is a cube 1 cm long on each side.

  25. Density Density is an intensive physical property of a substance. m V d =

  26. Sample Exercise 1.4 • A) Calculate the density of mercury if 1.00x102 g occupies a volume of 7.36 cm3. • B) Calculate the volume of 65.0 g of methanol if its density is 0.791 g/mL. • C) What is the mass in grams of a cube of gold (density = 19.32 g/cm3) if the length of the cube is 2.00 cm?

  27. Density Practice • 1. Calculate the density of a 374.5 g sample of copper if it has a volume of 41.8 cm3. • 2. A student needs 15.0 g of ethanol for an experiment. If the density of ethanol is 0.789 g/mL, how many mililiters of ethanol are needed? • 3. What is the mass of 25.0 mL of mercury if the density is 13.6 g/mL?

  28. Metric System Prefixes convert the base units into units that are appropriate for the item being measured.

  29. Temperature By definition temperature is a measure of the average kinetic energy of the particles in a sample.

  30. Temperature In scientific measurements, the Celsius and Kelvin scales are most often used. The Celsius scale is based on the properties of water. 0C is the freezing point of water. 100C is the boiling point of water.

  31. Temperature The Kelvin is the SI unit of temperature. It is based on the properties of gases. There are no negative Kelvin temperatures. K = C + 273.15

  32. Temperature The Fahrenheit scale is not used in scientific measurements. F = 9/5(C) + 32 C = 5/9(F − 32)

  33. Temperature Practice • Ethylene glycol, a major ingredient in antifreeze, freezes at -11.5ºC. What is the freezing point in Kelvin and ºF?

  34. 1.5 Uncertainty in Measurement

  35. Uncertainty in Measurements Different measuring devices have different uses and different degrees of accuracy.

  36. 3.1

  37. Significant Figures The term significant figures refers to digits that were measured. When rounding calculated numbers, we pay attention to significant figures so we do not overstate the accuracy of our answers.

  38. Significant Figures All nonzero digits are significant. Zeroes between two significant figures are themselves significant. Zeroes at the beginning of a number are never significant. Zeroes at the end of a number are significant if a decimal point is written in the number. Exact numbers are assumed to have an infinite number of sig figs

  39. Sample Exercise 1.5 • What difference exists between the measured values 4.0 g and 4.00 g? • A balance has a precision of ±0.001 g. A sample that has a mass of about 25 g is placed on this balance. How many significant figures should be reported for this measurement?

  40. Significant Figure Practice • How many significant figures are in the following: • A) 4.003 • B) 5000 • C) 0.00135 • D) 0.1270 • E) 6.023 x 1023 • F) 3.549 • G) 2.3 x 104

  41. Significant Figures When addition or subtraction is performed, answers are rounded to the least significant decimalplace. When multiplication or division is performed, answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation.

  42. Operations with Significant Figures Practice • Calculate the volume of a box with the following dimensions: 15.5 cm, 27.3 cm and 5.4 cm. Report your answer to the correct number of significant figures. • Calculate: 212.2 + 26.7 + 402.09 • It takes 10.5 s for a sprinter to run 100.00 m. Calculate the average speed in m/s.

  43. Sample Exercise 1.8 • A gas at 25ºC fills a container whose volume is 1.05 x 103 cm3. The container plus the gas have a mass of 837.6 g. The container when emptied of all gas has a mass of 836.2 g. What is the density of the gas at 25ºC? • To how many significant figures should the mass of the container be measured (with and without the gas) for density to be calculated to three significant figures?

  44. Accuracy, Precision, and Error Just because a measuring device works, you cannot assume it is accurate. The scale below has not been properly zeroed, so the reading obtained for the person’s weight is inaccurate. 3.1

  45. Accuracy versus Precision Accuracy refers to the proximity of a measurement to the true value of a quantity. Precision refers to the proximity of several measurements to each other.

  46. Determining Error The accepted value is the correct value. The experimental value is the value measured in the lab. The difference between the experimental value and the accepted value is called the error. 3.1

  47. Accuracy, Precision, and Error The percent error is the absolute value of the error divided by the accepted value, multiplied by 100%. 3.1

  48. Practice Problem A technician experimentally determined the boiling point of octane to be 124.1ºC. The actual boiling point of octane is 125.7ºC. Calculate the error and percent error.

  49. 1.6 Dimensional Analysis

  50. Dimensional Analysis We use dimensional analysis to convert one quantity to another. Most commonly dimensional analysis utilizes conversion factors (e.g., 1 in. = 2.54 cm) 1 in. 2.54 cm 2.54 cm 1 in. or

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